Machines such as dozers, loaders, excavators and other types of machinery typically include a hydro-mechanical power transmission system to transfer power, e.g., torque and rotational speed generated by a power source, to one or more connected loads, such as a machine tool or other implement. A major component of these hydro-mechanical power transmission systems is a hydraulic pump. The hydraulic pump or pumps generate pressurized hydraulic fluid that is used to operate the components of the machine.
One type of hydraulic pump is a hydraulic piston pump that includes a pump housing defining a pump cavity housing one or more piston pumps. The hydraulic piston pumps each include reciprocating pistons arranged within corresponding piston chambers of a pump barrel that is operably connected to a rotating shaft so that the pump barrel and the pistons rotate with the shaft. The pistons within each pump extend outwardly from one end of the corresponding pump barrel and impinge on a swash plate. As the barrel and the pistons rotate and the swash plate remains stationary, the pistons reciprocate within the piston chambers with a stroke length determined by the orientation of the swash plate, and thereby causing hydraulic fluid to be drawn into the pump barrel on the expansion strokes of the pistons and to be discharged from the pump barrel under pressure on the compression strokes.
In one typical arrangement for a piston pump, semi-circular cradle bearings having concave bearing surfaces are installed in the housing between the housing wall and the swash plate to facilitate rotation of the swash plate within its designed range of motion. The swash plate has corresponding convex bearing surfaces that are received by the cradle bearings and are slidable therein. At any point in the rotation of the pump barrel and pistons about the rotational axis of the shaft, four to five pistons in a nine piston pump are performing compression strokes and are under pressure at the same time due to the to the compression of the hydraulic fluid. The pressure force is transmitted through the pistons to the swash plate and ultimately to the cradle bearings and the housing wall. The force causes stresses in the interfacing elements, particularly where an edge of one element bears on a surface of the adjoining element.
In an exemplary piston pump disclosed in Int'l Publ. No. WO 2009/083153 A1 by Breuer and published on Jul. 9, 2009, a piston pump includes bearing elements configured to compensate for deflection of a pivoting base or swash plate. A pivoting-base mounting of the axial piston pump includes a housing, a pivoting base or swash plate, and a pivoting bearing region that is formed by the housing and the pivoting swash plate. The pivoting swash plate and/or the housing and/or the bearing element that is arranged in the pivoting bearing region are of deformable configuration in such a way as to compensate for a deflection of the pivoting swash plate. The publication discusses deformations in the elements being caused by stresses, but does not discuss reduction of stresses caused by forces from the pistons. In view of this, a need exists for configuring the components of the hydraulic piston pump in a manner that reduces the stresses created in the interfacing elements, and in particular in the cradle bearings.